1. Field of the Invention
The invention relates to data storage systems. Specifically, the invention relates to apparatus, systems, and methods for communicating control messages between a first device and a second device.
2. Description of the Related Art
High density, removable media storage libraries are used to provide large quantities of storage in a computer system. Typically, such data storage systems are employed for backup or other secondary storage purposes, but may be used as primary storage in circumstances that are conducive to sequential data access and the like.
FIG. 1 illustrates a block diagram of a conventional system 100 that includes a removable media storage library. The system 100 includes an Automated Library Unit (ALU) 102 and at least one host 104. Each host 104 may be a mainframe computer. Alternatively, the hosts 104 may be servers or personal computers using a variety of operating systems.
The ALU 102 includes a library manager (LM) 106, one or more data drive devices, which may be tape drive units 108, an accessor 110, and a plurality of media cartridges 112. The plurality of media cartridges 112 may be stored in one or more media cartridge storage bins (not shown).
The LM 106, which includes at least one computing processor, is interconnected with, and controls the actions of, the tape drive units 108 and the accessor 110. The LM 106 typically also includes one or more hard disk drives (not shown) for memory storage, as well as, a control panel or keyboard (not shown) to provide user input. The control panel may be a computer in communication with the LM 106 so that a user can control the operating parameters of the automated tape library unit 102 independently of the host 104.
FIG. 1 illustrates three tape drive units 108a, 108b, and 108c. The system 100 may include a number of tape drive units 108. The tape drive units 108 may share one single repository of cartridges 112. Alternatively, the tape drive units 108 may independently correspond to and utilize multiple repositories of cartridges 112. The tape drive units 108 may advantageously be distributed over multiple locations to decrease the probability that multiple tape drive units 108 will be incapacitated by a disaster in one location.
The accessor 110 may be a robotic arm or other mechanical device configured to transport a selected cartridge 112 between a storage bin and a tape drive unit 108. The accessor 110 typically includes a cartridge gripper and a bar code scanner (not shown), or similar read system, mounted on the gripper. The bar code scanner is used to read a volume serial number (VOLSER) printed on a cartridge label affixed to the cartridge 112. In alternative embodiments, the tape drive units 108 may be replaced by optical disk drives or other magnetic drives. Similarly, the cartridges 112 may contain magnetic media, optical media, or any other removable media corresponding to the type of drive employed.
Generally, the host 104 connects via a data path 114 directly to the tape drive units 108. The data path 114 may comprise a storage area network (SAN) or similar communications channel. The data path 114 serves to rapidly transfer large quantities of data between two devices. Accordingly, the data path 114 uses high speed protocols optimized to move data such as Fibre Channel, Enterprise System Connection® (ESCON), Fiber Connection (FICON) channel, Small Computer System Interface (SCSI), and the like. Of course the data path 114 may include other controllers, switches, and the like for supporting the data transfer protocol which have been omitted for clarity. The data path 114 may comprise a network such as a storage area network (SAN), a local area network (LAN), wide area network (WAN), or a different type of network, such as the Internet. Alternatively, the data path 114 may comprise a direct connection between the host 104 and the tape drive units 108.
The host 104 communicates control information over a control path 116 to the LM 106. The control path 116 may also be referred to as a host control path 116 because instructions generally originate from the host 104 and are directed to the LM 106. Of course instructions may also flow from the LM 106 to the host 104.
Conventional systems 100 also include separate control links 118. The control links 118 and control path 116 are shown as dashed lines to indicate that the host 104 and LM 106 transmit and receive control signals, rather than data to be transferred to the tape drive units 108 and/or the accessor 110. Data for storage or retrieval may instead be transmitted directly between the host 104 and the tape drive units 108 via the data path 114.
Generally a control path 116 and control links 118 comprise physical cables such as RS-232 cables and employ conventional serial protocols such as TCP/IP or other protocols used on a LAN. Each control link 118a, 118b, 118c between a tape drive 108 and the LM 106 requires a separate physical cable connected on each end to a separate physical communication port.
Unfortunately, the control links 118 limit the capabilities of the automated library unit 102. Specifically, each control link 118 typically has a length limitation and must have a separate physical communication port on the LM 106. Consequently, the LM 106 will only support a number of tape drives 108 corresponding to the maximum number of physical communications (minus two for the host control path 116 and the control link 118 to the accessor 110). The communication links 118 may be made from different kinds of cable for example, RS-232, RS-422, or the like. However, these cables are operable up to a maximum length. Accordingly, the tape drives 108a must be located relatively close to the LM 106 to properly exchange control information. Furthermore, the cable for the control links 118 increases the cost of the system 100. Maintaining and troubleshooting faulty cables for control links 118 may also be difficult due the number of cables and similarity in appearance.
Accordingly, what is needed is an apparatus, system, and method to overcome the inefficiencies of conventional data storage systems that include control links 118 between the LM 106 and the tape drive units 108. In particular, the apparatus, system, and method should replace the physical control links 118 with a virtual control link between the LM 106 and tape drives 108 using the existing control path 116 and data path 114. Such a virtual control link should permit any number of tape drives 108 to communicate control information with the LM 106. In addition, the apparatus, system, and method should provide the virtual control link such that modifications to the control information protocol do not require corresponding modifications to the virtual control link. Such an apparatus, system, and method is provided herein.